DE102016008821A1 - Dialysis machine and method for correcting the blood flow value - Google Patents

Abstract

The invention relates to a dialysis machine with an extracorporeal blood circulation, in which a dialyzer, a blood pump and an arterial pressure sensor are arranged, wherein the dialysis machine further has a compensation device, by means of which the set value for the blood flow through the extracorporeal circulation using the arterial The blood pressure can be corrected to a compensated value, wherein the dialysis machine further has detection means, which are adapted to detect whether the arterial pressure sensor is connected to the extracorporeal blood circulation or not, and that the dialysis machine has an estimation unit, which is designed Estimate the value of the arterial blood pressure, if detected by the detection means that the arterial pressure sensor is not connected to the extracorporeal blood circulation.

Description

The present invention relates to a dialysis machine with an extracorporeal blood circulation, in which a dialyzer, an arterial pressure sensor and a blood pump are arranged, wherein the dialysis machine further has a compensation device, by means of which the set value for the blood flow through the extracorporeal circuit using the arterial blood pressure can be corrected to a compensated value.

From the prior art dialysis machines are known which have an arterial pressure sensor in the extracorporeal circuit between the arterial needle and the blood pump. This serves to detect the arterial pressure in a dialysis treatment. The pressure sensor is connected via a pressure discharge to an arterial line of the extracorporeal blood circulation. The pressure drain typically includes a transducer protector (hereinafter "TP") that protects the pressure sensor from contact with the patient's blood. This is usually achieved by a hydrophobic membrane in the TP.

The TP thus serves to separate the blood side from the machine side and prevents contamination of the machine by blood flowing through the extracorporeal circuit. Otherwise, this can lead to cross-contamination between patients.

The TP is usually in a pressure discharge, i. H. z. B. in a piece of tubing that connects the extracorporeal blood circulation, in particular its arterial portion, with the arterial pressure sensor. The TP typically includes a hydrophobic membrane that keeps the blood away from the pressure sensor.

Known dialysis machines furthermore have a compensation device which, using the value of the arterial blood pressure, corrects the blood flow through the extracorporeal circulation set by a user of the dialysis machine, the treatment being based on the corrected value. This correction is necessary because due to an ovalized tube cross-section upstream of the blood pump, the calculated effective blood flow may not correspond to the actual, set pumping rate.

The arterial pressure in the blood is thus needed to provide a value for compensated blood flow. It is known from the prior art to determine the compensated, ie corrected blood flow Q _b from the adjusted blood flow Q _{b, set} according to the following relationship. Q _b = Q _{b, set} (α + β · P _a ) (1)

Where: α = 1.0 and β = 0.00057; Q in [ml / min], P _a in [mmHg]

If the arterial pressure discharge is not connected, the atmospheric pressure (P _a = 0 mmHg) is always measured at the arterial pressure sensor. This means according to equation (1) that the indicated blood flow Q _{b is} equal to the adjusted blood flow Q _{b, set} , that is, a correction does not take place. This, in turn, may cause the displayed value of Q _b to exceed the user-set value Q _{b, set} by more than 11%. As a result, the medical prescription or the accumulated purified blood volume for a dialysis treatment is not reached because the real effective blood flow rate is smaller than that set by the user.

From practice it is known that treatments are performed without a connected pressure discharge and thus without connected pressure sensor, which is a misuse of the dialysis machine. Nevertheless, a realistic indication of the actual blood flow should also be possible for this case.

From the WO 02/04044 A1 For the detection of arterial enema problems during extracorporeal blood treatment, it is known to measure the amplitude of the periodic fluctuations of the pressure due to the revolutions of the blood pump in the venous blood line and to compare them with a threshold value. Infeed problems are closed when the threshold is exceeded. In a dialysis machine which has a dialysis fluid system, instead of the pressure in the venous blood line, the pressure in the dialysis fluid system can also be monitored. An arterial blood pressure measurement does not have to be done. The US 2013/072846 A1 describes a method for determining the blood pressure upstream of the blood pump by measuring the blood pressure downstream of the blood pump.

The present invention has the object, a dialysis machine of the type mentioned in such a way that even with not connected arterial pressure sensor, especially when not connected arterial pressure derivative, the indication of a realistic value for the blood flow is possible.

This object is achieved by a dialysis machine having the features of claim 1.

Thereafter, it is contemplated that the dialysis machine further comprises detecting means configured to recognize whether or not the arterial pressure sensor is connected to the extracorporeal blood circuit, and that the dialysis machine has an estimation unit that is configured To estimate the value of the arterial blood pressure (Pa), if it is detected by the detection means that the arterial pressure sensor is not connected to the extracorporeal blood circulation, which may be caused, for example, that the arterial pressure discharge was not used.

The present invention is thus based on the idea to be able to provide the most reliable possible compensation or correction of the set blood flow in the extracorporeal circulation even in the absence of the connection of the pressure sensor to the extracorporeal circuit. The purpose of the detection means is to determine whether the arterial pressure sensor is connected or not and the estimation means have the task in the event that no arterial pressure sensor is connected to provide a replacement value for the (non-measured) arterial blood pressure in the extracorporeal circuit.

By a "connected pressure sensor" is meant that the pressure sensor is connected to the extracorporeal circuit so that it is able to measure the pressure in the extracorporeal circuit.

Failure to connect a pressure sensor may be due to the lack of pressure discharge, i. H. the hose or line piece that connects the extracorporeal circuit to the pressure sensor and in which the TP is usually located.

This can then be used to make the compensation of blood flow. The compensated, d. H. corrected value for the blood flow can then be used as a basis for the treatment, displayed etc.

In a conceivable embodiment, it is provided that the said compensation device is designed to determine the value for the compensated blood flow according to equation (1) above. Using this equation, not the measured, but the estimated arterial blood pressure is used for P _a .

The estimation unit may be designed to estimate the arterial blood pressure to a constant value, preferably to the value of P _a = -200 mmHg. Regardless of the set blood flow z. B. according to equation (1) with a constant value for P _a a value for Q _{b are} determined. The exemplified value of -200 mmHg corresponds approximately to the pressure value which results with a blood flow of Q _{b, set} = 300 ml / min in a normal dialysis treatment.

In a further embodiment of the invention, the estimation unit is designed to estimate the arterial blood pressure as a function of the user-set blood flow Q _{b, set} , wherein a memory or other calculation means is provided in which a relationship between the arterial blood pressure P _a and the user-set Blood flow Q _{b, set is} deposited. For example, a curve or a table is conceivable for the relationship P _a = f (Q _{b, set} ). On the basis of these values, which can be stored in a software, the value for P _a can then be determined from Q _{b, set} and finally the blood flow z. B. calculated according to equation (1).

The estimation unit can furthermore be designed in such a way that further parameters play a role in the aforementioned relationship between the set blood flow and the arterial blood pressure. For example, a property of the cannula used, such as, for example, its outer diameter and / or the hematocrit value HKT of the blood, may be considered.

For a given arterial blood tube, the relationship between the estimated arterial blood pressure and the adjusted blood flow can thus still be influenced by the dialysis cannula and / or by the hematocrit value of the blood. In principle, a set of curves or tables for the function P _a = f (Q _{b, set} ) depending on the dialysis cannula and the hematocrit can be determined experimentally and stored in the software. The type of dialysis cannula and the hematocrit value can be specified by user input via a user interface before dialysis treatment. It is also conceivable that the hematocrit value is measured during dialysis by a dialysis machine and then the measured value is used accordingly.

• – 16 G mit 1,6 mm Außendurchmesser
• – 17 G mit 1,5 mm Außendurchmesser
• – 15 G mit 1,8 mm Außendurchmesser.

Typical dialysis needles are:

• - 16 G with 1.6 mm outside diameter
• - 17 G with 1.5 mm outer diameter
• - 15 G with 1.8 mm outside diameter.

Typical values for the hematocrit value range between 27 and 42%.

For a realization of this embodiment of the invention, it is advantageous to determine the relationship between the estimated arterial blood pressure and the adjusted blood flow in a typical dialysis cannula e.g. At a 16G needle and at a typical hematocrit level, e.g. B. 35% to determine and then deposit in the software.

In a further embodiment of the invention it is provided that the estimation unit is formed, the arterial blood pressure in dependence of the measured venous blood pressure in the extracorporeal blood circulation.

This embodiment of the invention will be explained in more detail with reference to the single figure, which represents an extracorporeal blood circulation of a hemodialysis machine according to the invention.

In this case, the reference numeral 16 the blood access, which may be formed as a fistula or shunt and the reference numerals 15a and 15b the arterial and venous needle.

From the arterial needle 15a the blood passes through the blood tube 14 about the arterial pressure derivation 1c to the arterial TP by the reference numeral 1b to which the arterial pressure sensor 1a connected to measure the arterial pressure P _a . Downstream of it is the blood pump 3 and downstream of the blood pump, the heparin pump 4 , Between the heparin pump 4 and the dialyzer is the arterial bubble trap 5 ,

The dashed line in Fig. 1b represents the transition from the tube system to the dialysis machine. There, the pressure discharge is thus connected to the pressure sensor, e.g. B. with a Luer-lock connection.

The dialyzer is designated by the reference numeral 6 and is characterized by a semi-permeable membrane 7 , preferably by a hollow fiber bundle, divided into a dialysate chamber and a blood chamber, wherein the Dialysatzulauf to the dialysate chamber 8th and the dialysate drain 9 are connected.

Downstream of the dialyzer 6 is the venous drip chamber 10 with a level detector 11 , To the venous drip chamber 10 connected is the venous pressure discharge 2c used in conjunction with the venous pressure sensor with the reference numeral 2a for measuring venous blood pressure P _v . Into the venous pressure derivation is the venous TP with the reference numeral 2 B brought in.

Downstream of the venous drip chamber 10 there is a venous clamp 12 , by means of which the blood tube can be shut off and the optical detector 13 to detect air bubbles in the blood.

About the venous needle 15b the blood gets back into the fistula or into the shunt 16 ,

In the following it will now be shown how, based on the venous blood pressure P _v , the z. In or at the venous drip chamber 10 can be measured, the arterial blood pressure P _a can be deduced.

By analogy with Ohm's law, the arterial side of the extracorporeal blood circulation Q _b = (P _{f, a} -P _a ) / R _a . Solving this equation for P _a yields: P _a = P _{f, a} - Q _b · R _a (2 ')

On the venous side of the extracorporeal blood circulation, Q _b - Q _UF = (P _v -P _{f, v} ) / R.

Solving this equation for venous pressure yields: P _v = (Q _b - Q _UF ) * R _v + P _{f, v} (3 ')

Adding the equations (2 ') and (3') results in: P _a + P _v = Q _b * (R _v -R _a ) + (P _{f, a} + P _{f, v} ) -Q _UF * R _v (4 ')

In the context of the present invention: P _{f is} the fistula pressure, P _{f, a is} the fistula pressure at the site of the arterial dialysis needle, P _{f, v is} the fistula pressure at the site of the venous dialysis needle, P _{a is} the arterial pressure upstream of the blood pump, P _{v is} the venous pressure at the venous drip chamber, P _{v, 0} the measured venous pressure at stopping the blood pump and at open venous clamp, Q _{b, set} the adjusted blood flow, Q _b the compensated blood flow, Q _UF the ultrafiltration rate, R _a the flow resistance between the arterial pressure discharge 1c and the peak of the arterial needle, R _v the flow resistance between the venous drip chamber and the tip of the venous needle, and MAP the mean measured arterial blood pressure of the dialysis patient.

The length of the arterial tubing section between the arterial pressure drain and the arterial needle connector is nearly identical to the length of the venous tubing section between the venous drip chamber and the venous needle connector. This length can be for example about 190 cm. Taking into account the fact that in a routine dialysis, arterial and venous needles of the same type, e.g. B. 16 G are used, the flow resistance of the above hose sections are also almost identical, that is, it holds in equation (4 ') R _a = R _v . This results in: P _a = (P _{f, a} + P _{f, v} ) - Q _UF * R _v -P _v (5 ')

The ultrafiltration rate Q _UF in dialysis is relatively small. Neglecting this value, or measuring P _a with the ultrafiltration switched off, equation (5 ') yields the following relationship: P _a = (P _{f, a} + P _{f, v} ) -P _v (6 ')

The pressures in the shunt or in the fistula can be estimated as follows:
For the case of fistula: P _{f, a} = 0.20 · MAP P _{f, v} = 0.15 · MAP P _{f, a} = 1.33 · P _{f, v}

The following relationships apply to the shunt: P _{f, a} = 0.55 · MAP P _{f, v} = 0.35 · MAP P _{f, a} = 1.57 · P _{f, v}

This results from equation (6 ') in the case of fistula P _a = 0.35 · MAP - P _v (7 ') such as P _a = 2.33 · P _{f, v} - P _v (8 ')

From equation (6 ') results in the shunt case _V (9 ') P - P _a = 0.90 · MAP such as P _a = 2.57 · P _{f, v} - P _v (10 ')

In hemodialysis, it is mandatory to measure the blood pressure of a patient. The mean arterial blood pressure MAP in equations (7 ') and (9') is therefore known. This MAP value can either be determined automatically by a blood pressure monitor (BPM) integrated into the dialysis machine or entered manually via a user interface. In these cases, the sought value P _a for measured P _{v can be determined} according to equation (7 ') or according to equation (9').

As can be seen from the equations (8 ') and (10'), the determination of P _a in these cases requires the value P _{f, v} , which in a further preferred embodiment is represented by the relation P _{f, v} = P _v0 + 14.72 can be determined.

This relationship is as follows:
After connecting the patient to the extracorporeal blood circulation, the blood pump is started and the patient's blood is delivered to the extracorporeal bloodstream. Once the optical detector detects the blood at the venous drip chamber, the blood pump is stopped and the venous clamp 12 closed. The user is then asked if the dialysis treatment should be started. If the venous clamp is briefly opened in this case, the venous pressure is measured as P _v0 .

Taking into account the hydrostatic pressure between the fistula access to the patient's arm and the venous pressure discharge 2c the value for P _{f, v is} calculated after P _{f, v} = P _v0 + r * g * H (11 ')

Here, r is the water density and is 1000 kg / m ³ , H is the height difference between the fistula access and the venous pressure derivation 2c , z. B. 20 cm and g is the gravitational acceleration (9.81 m / s ² ). From equations (8 '), (10') and (11 '), fistula results P _a = 2.33 × (P _v0 + r × g × H) -P _v (12 ') and for the shunt P _a = 2.57 × (P _v0 + r × g × H) -P _v (13 ')

With a height difference of 0.2 m, this results in:
r · g · H = 1000 · 9.81 · 0.2 = 14.72 mmHg.

Substituting this value into equation (11 ') results in the said relationship, namely P _{f, v} = P _v0 + 14.72 [mmHg] (14 ')

Knowing this value as well as the venous blood pressure, the value P _a can be determined from equations (8 ') and (10').

In a further embodiment of the invention it is provided that the detection means are designed to determine the signal detected by means of the arterial pressure sensor, a running averaging and variance calculation over a certain period of time, for. B. one minute, and to close on the basis of the evaluation of mean and variance on the presence or absence of a connected arterial pressure sensor. The lack of this connection can be attributed, for example, to the fact that the arterial pressure discharge (with the TP possibly contained therein) is not used, so that the arterial pressure sensor can not measure the pressure in the extracorporeal blood circulation.

In an alternative or additionally applicable embodiment, it is provided that the recognition means are designed to determine the pressure signal detected by the arterial pressure sensor, to start and stop the blood pump, while the blood tube system is filled, to determine the signal change of the arterial blood pressure, and based on the absence or presence of the arterial pressure discharge or the connection of the arterial pressure sensor.

If no connected pressure sensor is detected, the blood flow compensation is performed using the methods described above, preferably using equation (1), using P _a an estimated value according to the invention.

Otherwise, the measured value for P _a is used.

The present invention further relates to a method for correcting a set value for the blood flow using the arterial blood pressure to a compensated value in a dialysis machine with an extracorporeal blood circulation, in which a dialyzer, a blood pump and an arterial pressure sensor are arranged, is detected, whether the pressure sensor is connected to the extracorporeal circuit or not and where an arterial blood pressure value is estimated, if it is determined that this is not the case. In this case, the value for the compensated blood flow can be determined according to equation (1) above.

Arterial blood pressure can be estimated to be a constant value, such as -200 mmHg. It is also possible to estimate the arterial blood pressure as a function of the blood flow set by the user, wherein a corresponding relationship between the arterial blood pressure and the adjusted blood flow is stored in software or in a memory or by a calculation unit. Other parameters may play a role here, in particular the type of dialysis cannula used and in particular its outer diameter and / or the measured or entered hematocrit value of the blood.

It is also conceivable, as stated above, that the arterial blood pressure is estimated as a function of the venous blood pressure in the extracorporeal circulation.

It is conceivable that the following relationships apply: P _a = 0.35 · MAP - P _v , P _a = 2.33 · P _{f, v} - P _v respectively. P _a = 0.90 · MAP - P _v , P _a = 2.57 · P _{f, v} - P _v

For the derivation of these relationships, we refer to the above statements.

In a further embodiment of the method, it is provided that the value P _{f, v is} calculated after blood is introduced into the extracorporeal circuit to the venous pressure sensor, then the venous pressure clamp is opened and then the venous blood pressure P _{v0 is} measured when the blood pump is stationary , The value of P _{f, v} results from the relation P _{f, v} = P _v0 + 14.72. To determine this equation, we also refer to the above statements.

In a further embodiment of the method it is provided that for detecting the presence or absence of the connection of the arterial pressure sensor, the pressure signal detected by the arterial pressure sensor is determined and is checked based on a running averaging and variance calculation over a certain period of time, whether the pressure sensor is connected or Not. It is also conceivable to determine the pressure signal detected by the arterial pressure sensor, while the blood pump is started and stopped again. The pressure signal provides information on the presence or absence of the connection of the arterial pressure sensor or the arterial pressure discharge.

In principle, it is conceivable that the detection of whether the pressure sensor is connected is based on the fact that the pressure sensor measures no pressure fluctuations, even though the blood pump is running, or that the blood pump delivers a pressure pulse which is not measured at the pressure sensor.

Further details and advantages of the invention will be explained in more detail with reference to an embodiment described in the drawing and in the following.

The sole figure shows an extracorporeal blood circulation, which is connected via a venous needle and an arterial needle to a fistula or to a shunt of the patient.

First, via a not shown in the drawing user interface of the dialysis machine, in which the extracorporeal blood circulation is used according to the figure, entered whether it is the blood access to a fistula or a shunt. Then, the input of the measured MAP, that is, the mean blood pressure of the patient takes place.

From the time of blood detection by the optical detector 13 be z. For example, every two minutes the values for P _a and P _{v are} segment _by segment evaluated to detect a non-connected pressure sensor or pressure derivative. If it is detected that both pressure sensors or pressure derivatives are connected, that is, the arterial and the venous, the blood flow is compensated according to equation (1), wherein for P _a the measured arterial blood pressure is used.

If it is determined that none of the pressure sensors, that is, neither the venous nor the arterial, are connected, a warning is issued asking the user to connect both pressure sensors. If it is determined that the venous pressure sensor is connected but the arterial pressure sensor is not, a warning is issued prompting the user to also connect the arterial pressure sensor. If this is not the case, the procedure continues as follows.

During normal dialysis treatment, the venous pressure of the blood in the extracorporeal circulation, that is to say P _{v, is} measured while the blood pump is running. Then, the formation of a running average of P _v .

According to equation (7 ') or according to equation (9'), the calculation, that is the estimation of P _a for the fistula or for the shunt takes place. Based on these values, the value for the compensated blood flow, that is Q _b , can then be determined by means of equation (1).

It is conceivable that this value is limited to the area 0.85Q _{b, set} ≤ Q _b ≤ Q _{b, set}

Preferably, the compensation method is performed exclusively for the active dialysis phase, that is, when blood is detected in the system, the blood pump is running and the dialysis is alarm-free. A compensation in the phase of preparation and reinfusion is conceivable, but in principle not necessary.

Finally, it should be noted that the term "a" or "an" used in the context of the invention encompasses a single of the elements concerned, but also a majority of these elements, that is to say, H. not necessarily equated with "a single one".

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• WO 02/04044 A1 [0010]
• US 2013/072846 A1 [0010]

Claims (15)

Dialysis machine with an extracorporeal blood circulation ( 1 ), in which a dialyzer ( 6 ), a blood pump ( 3 ) and an arterial pressure sensor ( 1a ), wherein the dialysis machine further has a compensation device, by means of which the set value for the blood flow (Q _{b, set} ) through the extracorporeal circuit ( 1 ) is correctable to a compensated value (Q _b ) using the arterial blood pressure (P _a ), characterized in that the dialysis machine further comprises recognition means arranged to detect whether the arterial pressure sensor ( 1a ) to the extracorporeal blood circulation ( 1 ) and that the dialysis machine has an estimation unit which is designed to estimate a value for the arterial blood pressure (P _a ) if the recognition means detects that the arterial pressure sensor ( 1a ) not to the extracorporeal blood circulation ( 1 ) connected. Dialysis machine according to claim 1, characterized in that the dialysis machine is designed such that a pressure discharge ( 1c ), which in the connected state, the arterial pressure sensor ( 1a ) with the extracorporeal blood circulation ( 1 ) and that the detection means are adapted to detect whether the pressure derivative ( 1c ) is connected or not. Dialysis machine according to claim 1 or 2, characterized in that the compensation device is designed to determine the value for the compensated blood flow (Q _b ) in [ml / min] according to equation (1): Q _b = Q _{b, set} (α + β · P _a ) (1), where α is 1.0 and β is 0.00057 and P _{a is used} as the value in [mmHg]. Dialysis machine according to one of the preceding claims, characterized in that the estimation unit is designed to estimate the arterial blood pressure (P _a ) to a constant value, preferably to the value - 200 mmHg and / or that the estimation unit is designed to increase the arterial blood pressure (P _a ). P _a ) as a function of the user-set blood flow (Q _{b, set} ), wherein a memory or a calculation unit is provided, in which / a relationship between the arterial blood pressure (P _a ) and the user-adjusted blood flow (Q _{b, set} ), wherein it is preferably provided that the estimation unit is designed such that in the said context as a further parameter a property of the dialysis cannula used and / or the hematocrit value (HKT) of the blood is received. Dialysis machine according to one of the preceding claims, characterized in that the estimation unit is designed to estimate the arterial blood pressure (P _a ) as a function of the venous blood pressure (P _v ) in the extracorporeal circuit, wherein it is preferably provided that the estimation unit is designed to determine arterial blood pressure (P _a ) in [mmHg] according to one of the relationships (P _v : venous blood pressure in the extracorporeal circulation; MAP: mean blood pressure; P _{f, v} : fistula pressure / shunt pressure at the site of the venous dialysis needle) P _a = 0.35 · MAP - P _v (2) P _a = 2.33 · P _{f, v} - P _v (3) P _a = 0.90 · MAP - P _v (4) P _a = 2.57 · P _{f, v} - P _v (5), where equations (2) and (3) for the use of a fistula and equations (4) and (5) for the use of a shunt are used. Dialysis machine according to claim 5, characterized in that the dialysis machine has a calculation unit for determining P _{f, v} and that this calculation unit is designed, after the introduction of blood into the extracorporeal circuit to the venous pressure sensor, a venous pressure clamp ( 12 ) and then to measure the venous blood pressure (P _v0 ) with the blood pump standing, and that the calculation unit is designed to determine the value for P _{f, v} in [mmHg] as follows: P _{f, v} = P _v0 + 14.72 (6) Dialysis machine according to one of the preceding claims, characterized in that the detection means are formed, which by means of the arterial pressure sensor ( 1a ), a running averaging and variance calculation over a certain period to perform and based on the evaluation of mean and variance on the presence or absence of the connection of the arterial pressure sensor ( 1a ) to the extracorporeal blood circulation ( 1 ) close. Dialysis machine according to one of the preceding claims, characterized in that the detection means are formed, which by means of the arterial pressure sensor ( 1a ), to start and stop the blood pump, to determine the change in arterial blood pressure (P _a ) and based on the presence or absence of the connection of the arterial pressure sensor ( 1a ) to the extracorporeal blood circulation ( 1 ) close. Method for correcting a set value for the blood flow (Q _{b, set} ) using the arterial blood pressure (P _a ) to a compensated value (Q _b ) in a dialysis machine with an extracorporeal blood circulation ( 1 ), in which a dialyzer ( 6 ), a blood pump ( 3 ) and an arterial pressure sensor ( 11 ), characterized in that it is detected whether the arterial pressure sensor ( 11 ) on the extracorporeal circuit ( 1 ) is connected or not, and that an arterial blood pressure (P _a ) value is estimated, if it is determined that the arterial pressure sensor ( 11 ) not on the extracorporeal circuit ( 1 ) connected. A method according to claim 9, characterized in that the value for the compensated blood flow (Q _b ) in [ml / min] is determined according to equation (1): Q _b = Q _{b, set} (α + β · P _a ) (1), where α is 1.0 and β is 0.00057 and P _{a is used} as the value in [mmHg]. A method according to claim 9 or 10, characterized in that the arterial blood pressure (P _a ) to a constant value, preferably to the value - 200 mmHg is estimated and / or that the arterial blood pressure (P _a ) in dependence of the user-adjusted blood flow ( Q _{b, set} ) is estimated, wherein a relationship between the arterial blood pressure (P _a ) and the user-set blood flow (Q _{b, set} ) is retrievably stored, wherein it is preferably provided that in the said context as a further parameter, a property of used dialysis cannula and / or the hematocrit value (HKT) of the blood. Method according to one of the preceding claims, characterized in that the arterial blood pressure (P _a ) is estimated as _a function of the venous blood pressure (P _v ) in the extracorporeal circuit, wherein it is preferably provided that the arterial blood pressure (P _a ) in [mmHg] is determined according to one of the relationships (P _v : venous blood pressure in the extracorporeal circulation, MAP: mean blood pressure, P _{f, v} : fistula pressure / shunt pressure at the site of the venous dialysis needle) P _a = 0.35 · MAP - P _v (2) P _a = 2.33 · P _{f, v} - P _v (3) P _a = 0.90 · MAP - P _v (4) P _a = 2.57 · P _{f, v} - P _v (5), where equations (2) and (3) for the use of a fistula and equations (4) and (5) for the use of a shunt are used. A method according to claim 12, characterized in that P _{f, v is} calculated, wherein after the introduction of blood into the extracorporeal circuit to the venous pressure sensor, a venous pressure clamp ( 12 ) and then the venous blood pressure (P _v0 ) is measured with the blood pump stopped, and the value of P _{f, v} in [mmHg] is then determined as follows: P _{f, v} = P _v0 + 14.72 (6) Method according to one of the preceding claims, characterized in that for the detection of the existing or non-existing connection of the arterial pressure sensor ( 1a ) to the extracorporeal circuit ( 1 ) through the arterial pressure sensor ( 1a a running averaging and variance calculation is performed over a certain period of time and based on the evaluation of mean and variance on the presence or absence of the connection of the arterial pressure sensor ( 1a ) to the extracorporeal circuit ( 1 ) is closed. Method according to one of the preceding claims, characterized in that for the detection of the presence or absence of the connection of the arterial pressure sensor ( 1a ) to the extracorporeal circuit ( 1 ) through the arterial pressure sensor ( 1a ), the blood pump is started and stopped again, the change in the arterial blood pressure (P _a ) is determined and based on the presence or absence of the connection of the arterial pressure sensor ( 1a ) to the extracorporeal circuit ( 1 ) is closed and / or that a pressure derivative ( 1c ), which in the connected state, the arterial pressure sensor ( 1a ) with the extracorporeal blood circulation ( 1 ) and that the detection of the presence or absence of the connection of the arterial sensor ( 1a ) is to the extracorporeal circuit in that it is recognized whether the pressure derivation ( 1c ) is connected or not.

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